Rubber composition and tire

ABSTRACT

Provided is a rubber composition for tire treads that is capable of producing tire treads for which abrasion resistance, rolling resistance, factory workability, and chipping resistance have been simultaneously improved, and a pneumatic tire manufactured using the same. The rubber composition according to the present invention includes 20 parts by mass to 100 parts by mass of carbon black combined with 100 parts by mass of a rubber component. The carbon black has a CTAB surface area of 60 m 2 /g to 105 m 2 /g, a 24M4DBP oil absorption of 70 cm 3 /100 g to 105 cm 3 /100 g, a N 2 SA/IA of 0.95 or less, and satisfies Expression (1). 
       TINT (%)+0.4×24 M 4 DBP  oil absorption (cm 3 /100 g)−0.5× CTAB  surface area (m 2 /g)&gt;106   (1)

TECHNICAL FIELD

The present invention is related to a rubber composition and a tire, andin particular to a rubber composition for tire treads that is capable ofproducing tire treads for which abrasion resistance, rolling resistance,factory workability, and chipping resistance have been simultaneouslyimproved (a rubber composition for tire treads that is capable ofproducing tire treads with low heat-buildup, excellent abrasionresistance, and high rebound resilience), and a pneumatic tiremanufactured using the same.

BACKGROUND ART

There is demand for a tire tread (tread rubber), where the tire contactsthe ground, to have both excellent resistance to abrasion while running(abrasion resistance) and little hysteresis loss, which is generatedupon deformation of rubber while running (rolling resistance), yet it isknown that there exists a trade-off between these properties.

The properties of the tire tread are greatly affected by the physicalproperties of carbon black combined with the rubber composition for tiretreads (for example, the specific surface area, structure, surfacetexture, and the like).

For example, if carbon black with a large specific surface area (smallprimary particle diameter) is combined with the rubber composition fortire treads, the abrasion resistance improves, yet problems occur suchas increased rolling resistance, increased heat buildup due to adifficultly for carbon black to diffuse in the rubber composition fortire treads, and reduced factory workability due to a great increase inthe unvulcanized rubber viscosity of the rubber composition for tiretreads.

Furthermore, if carbon black with a high structure is combined with therubber composition for tire treads, the abrasion resistance improves,yet problems occur such as higher rolling resistance, reduced factoryworkability due to a great increase in the unvulcanized rubber viscosityof the rubber composition for tire treads, reduced chipping resistanceof a tire in which the rubber composition for tire treads is used, andfurthermore an increase in heat buildup.

In order to solve these problems, the combination of carbon black havingspecific properties with the rubber composition for tire treads has beenexamined (for example, see JP5-230290A (PTL 1)).

A problem remains, however, in that the abrasion resistance, rollingresistance, factory workability, and chipping resistance of the tiretread cannot be simultaneously improved.

CITATION LIST Patent Literature

PTL 1: JP5-230290A

SUMMARY OF INVENTION

It is an object of the present invention to provide a rubber compositionfor tire treads that is capable of producing tire treads for whichabrasion resistance, rolling resistance, factory workability, andchipping resistance have been simultaneously improved, and to provide apneumatic tire manufactured using the same.

As a result of intensive study to achieve the above object, the inventordiscovered that the above object can be achieved by using a rubbercomposition containing 20 parts by mass to 100 parts by mass of carbonblack combined with 100 parts by mass of a rubber component, the carbonblack having a CTAB surface area of 60 m²/g to 105 m²/g, a 24M4DBP oilabsorption of 70 cm³/100 g (70 ml/100 g) to 105 cm³/100 g (105 ml/100g), a N₂SA/IA of 0.95 or less, and satisfying Expression (1). In otherwords, as a result of intensive study to achieve the above object, theinventor discovered that when the specific surface area (CTAB) and thestructure (24M4DBP) of carbon black increase or decrease, the value ofthe tint strength (TINT) also increases or decreases, yet the surfacearea (CTAB), structure (24M4DBP), and value of the tint strength (TINT)exhibit a predetermined relationship, and when using a rubbercomposition in which the ratio N₂SA/IA of the nitrogen adsorptionspecific surface area N₂SA to the iodine absorption number IA satisfiesa certain condition, the above object can be achieved. The presentinvention was completed based on these discoveries.

In other words, the rubber composition according to the presentinvention includes 20 parts by mass to 100 parts by mass of carbon blackcombined with 100 parts by mass of a rubber component. The carbon blackhas a CTAB surface area of 60 m²/g to 105 m²/g, a 24M4DBP oil absorptionof 70 cm³/100 g to 105 cm³/100 g, a N₂SA/IA of 0.95 or less, andsatisfies Expression (1).

TINT (%)+0.4×24M4DBP oil absorption (cm³/100 g)−0.5×CTAB surface area(m²/g)>106   (1)

The carbon black preferably has a CTAB surface area of 90 m²/g to 105m²/g.

The carbon black preferably has a 24M4DBP oil absorption of 85 cm³/100 gto 105 cm³/100 g.

A tire according to the present invention includes a tire treadmanufactured using the rubber composition according to the presentinvention.

According to the present invention, it is possible to provide a rubbercomposition for tire treads that is capable of producing tire treads forwhich abrasion resistance, rolling resistance, factory workability, andchipping resistance have been simultaneously improved, and to provide apneumatic tire manufactured using the same.

BRIEF DESCRIPTION OF DRAWINGS

The present invention will be further described below with reference tothe accompanying drawings, wherein:

FIG. 1 is a cross-sectional diagram of a carbon black production device.

DESCRIPTION OF EMBODIMENTS

The following describes the present invention in detail.

Rubber Composition

The rubber composition according to the present invention includes atleast a rubber component and carbon black, and as necessary, may furtherinclude other components such as zinc oxide, stearic acid, across-linking agent, a cross-linking promoter, and the like.

Rubber Component

The rubber component is not particularly limited and may be selected inaccordance with the purpose. Examples include a diene rubber such asnatural rubber (NR), polyisoprene rubber (IR), polybutadiene rubber(BR), styrene-butadiene copolymer rubber (SBR), acrylonitrilebutadienerubber (NBR), and the like. One of these rubbers may be used alone, ortwo or more may be used in combination.

Carbon Black

The carbon black is not particularly limited and may be selected inaccordance with the purpose, as long as the CTAB surface area is 60 m²/gto 105 m²/g, and preferably 90 m²/g to 105 m²/g.

If the CTAB surface area is less than 60 m²/g, the abrasion resistancedecreases, and upon exceeding 105 m²/g, neither rolling resistance norfactory workability can be obtained. Conversely, a CTAB surface areawithin the above preferable range is advantageous by striking a balancebetween abrasion resistance, rolling resistance, and factoryworkability.

The CTAB surface area can, for example, be measured in compliance withthe method in ISO 6810.

Note that a small CTAB surface area for carbon black denotes that theprimary particle diameter of the carbon black is large.

The 24M4DBP oil absorption of the carbon black is not particularlylimited and may be selected in accordance with the purpose, as long asthe 24M4DBP oil absorption is 70 cm³/100 g to 105 cm³/100 g, andpreferably 85 cm³/100 g to 105 cm³/100 g.

If the 24M4DBP oil absorption is less than 70 cm³/100 g, the abrasionresistance decreases, and upon exceeding 105 m³/100 g, neither rollingresistance nor factory workability can be obtained. Conversely, a24M4DBP oil absorption within the above preferable range is advantageousby striking a balance between abrasion resistance, rolling resistance,and factory workability.

The 24M4DBP oil absorption can, for example, be measured in compliancewith the method in ISO 6894.

Note that a small 24M4DBP oil absorption for the carbon black denotesthat the carbon black has a reduced structure.

The N₂SA/IA value of the carbon black is not particularly limited andmay be selected in accordance with the purpose, as long as the value is0.95 or less, and preferably 0.88 to 0.95.

If N₂SA/IA is less than 0.88, the abrasion resistance may decrease,whereas upon exceeding 0.95, chipping resistance cannot be obtained.N₂SA/IA within the above preferable range is advantageous by makingabrasion resistance compatible with chipping resistance.

The nitrogen adsorption specific surface area (N₂SA) can, for example,be measured with a single-point method in compliance with ISO 4652-1,and the iodine absorption number IA can be measured in compliance withthe method in ISO 1304. The ratio thereof, N₂SA/IA, can then becalculated.

Note that a small value of N₂SA/IA for carbon black denotes a smallnumber of surface functional groups in the carbon black.

The TINT (tint strength) of the carbon black, the 24M4DBP oilabsorption, and the CTAB surface area are not particularly limited andmay be selected in accordance with the purpose, as long as they satisfyExpression (1).

TINT (%)+0.4×24M4DBP oil absorption (cm³/100 g)−0.5×CTAB surface area(m²/g)>106   (1)

Abrasion resistance cannot be obtained if the TINT, the 24M4DBP oilabsorption, and the CTAB surface area do not satisfy Expression (1).

The TINT (tint strength) can, for example, be measured in compliancewith the method in ISO 5435.

The compounding amount of carbon black is not particularly limited andmay be selected in accordance with the purpose, as long as thecompounding amount is 20 parts by mass to 100 parts by mass, andpreferably 30 parts by mass to 70 parts by mass, with respect to 100parts by mass of a rubber component in the rubber composition.

If the compounding amount of the carbon black is less than 20 parts bymass, the abrasion resistance decreases, whereas upon exceeding 100parts by mass, rolling resistance cannot be obtained. Conversely, acompounding amount within the above preferable range is advantageous bymaking abrasion resistance compatible with rolling resistance.

Method of Producing Carbon Black

The method for producing the carbon black used in the present inventionis not limited, so long as the carbon black has the above properties. Asmethods for producing carbon black, the furnace method, channel method,thermal method, acetylene method, and the like are well known, with thefurnace method being the most general.

The carbon black used in the present invention can, for example, beproduced by a furnace method using a cylindrical production devicehaving a first region (combustion region) for causing fuel andoxygen-containing gas, such as air, to combust and generate combustiongas; a second region (tapered region), narrower than the first region,for supplying raw material for the carbon black and generating carbonblack; and a third region (reaction region) larger than the chokeregion.

A preferred embodiment of the production device is described withreference to FIG. 1. The production device illustrated in FIG. 1includes a first region 1 (consumption region), a second region 2(tapered region), and a third region 3 (reaction region), as well as achoke 4 in a connecting portion between the second region 2 and thethird region 3.

As a raw material for carbon black, the second region 2 supplieshydrocarbons or the like to the combustion gas generated in the firstregion 1 and generates carbon black by causing the raw material mainlyto undergo thermal decomposition. The second region 2 gradually becomesnarrower than a connecting portion with the first region 1 and connectsto the choke 4 via a narrow cylindrical portion 5.

The second region 2 is provided with a raw material inlet 7 forsupplying hydrocarbons or the like into the production device as rawmaterial for carbon black. In order to supply the raw material into thesecond region 2 as evenly as possible, the raw material inlet 7 may beconfigured with a plurality of rows, such as the raw material inlets 7-1to 7-3 illustrated in FIG. 1, and each of the raw material inlets 7-1 to7-3 may be formed from a plurality of inlets.

The choke 4 provided in the connecting portion between the second region2 and the third region 3 is a portion for adjusting the particlediameter of the obtained carbon black. The length of the choke 4 may beset appropriately for the desired carbon black particle diameter. In thepresent invention, a length of approximately 200 mm to 600 mm ispreferable, with 300 mm to 500 mm being more preferable.

The third region 3 cools the combustion gas that passes through thechoke 4 along with the carbon black to approximately 1000° C. or less toobtain carbon black particles and is formed by a wide cylindricalportion 6 having a larger diameter than the choke 4. The combustion gasis cooled by supplying water or the like through a reaction stoppingfluid inlet 8. The reaction stopping fluid inlet 8 may be configuredwith a plurality of rows, such as the reaction stopping fluid inlets 8-1to 8-5 illustrated in FIG. 1.

The supply of fuel and of oxygen-containing gas, such as air, as well asthe amount of supplied raw material and the method of supplying these isnot particularly limited, yet the ratio of the diameter of the thirdregion 3 to the diameter of the choke 4 (the diameter of the thirdregion 3/the diameter of the choke 4) is preferably 1.8 or greater, morepreferably 2 or greater, and even more preferably 2.2 or greater. Theupper limit of the ratio of the diameter of the third region 3 to thediameter of the choke 4 is not particularly limited, but considering thesize of the production device, the ratio is preferably approximately 4or less, and more preferably 3.5 or less. Note that an example of apreferred embodiment of the method of producing carbon black has beendescribed, yet the carbon black of the present invention is not limitedto being obtained in this way.

Cross-Linking Agent

The cross-linking agent is not particularly limited and may be selectedin accordance with the purpose. Examples include sulfur, sulfide (sulfuroxide), and the like. One of these may be used alone, or two or more maybe used in combination.

Increasing the compounding amount of sulfur used as the cross-linkingagent increases resilience while preserving abrasion properties.

Cross-Linking Promoter

The cross-linking promoter is not particularly limited and may beselected in accordance with the purpose. Examples includeN,N′-dicyclohexyl-2-benzothiazolylsulfenamide, diphenylguanidine,dibenzothiazyldisulfide, N-t-butyl-2-benzothiazylsulphenamide(N-t-butyl-2-benzothiazolylsulfenamide), hexamethylenetetramine,N,N′-diphenylthiourea, trimethylthiourea, N,N′-diethylthiourea,1,3-diphenylguanidine, 2-mercaptobenzothiazole,N-cyclohexyl-2-benzothiazolylsulfenamide, and the like. One of these maybe used alone, or two or more may be used in combination.

Increasing the compounding amount of the cross-linking promoterincreases resilience by increasing the link density due tocross-linking.

Tire

A tire according to the present invention is not particularly limitedand may be selected in accordance with the purpose, as long as itincludes a tire tread manufactured using the rubber compositionaccording to the present invention. A pneumatic tire, however, ispreferable.

A customary method may be used as the method of producing the tire. Forexample, members normally used in tire production, such as a carcasslayer, belt layer, tread layer, and the like made from unvulcanizedrubber, may be layered onto a tire molding drum, and the drum may beextracted to yield a green tire. Next, the green tire can be vulcanizedaccording to a regular method, thereby producing a desired pneumatictire.

EXAMPLES

The following describes specific examples of the present invention, yetthe present invention is not limited to these examples.

Examples 1 to 3 and Comparative Examples 1 to 10 Preparation of RubberCompositions

In the proportions listed in Table 1 below, components were mixed in aBanbury mixer to prepare rubber compositions. The properties of thecarbon black were measured with the method below. Furthermore, thecarbon black was produced with an oil furnace method of production underthe conditions listed in Table 2, using a furnace manufactured by AsahiCarbon Co., Ltd.

Note that this furnace is a cylindrical production device having a firstregion 1 (diameter: 700 mm, length: 1000 mm) for causing fuel and air tocombust, a second region 2 (upstream end diameter: 700 mm, downstreamend diameter: 230 mm, length: 1200 mm) for supplying raw oil andgenerating carbon black, a choke 4 (diameter: 230 mm, length: 400 mm),and a third region (diameter: 576 mm, length: 5000 mm, ratio of reactionregion diameter/choke region diameter: 2.5).

Furthermore, in Comparative Example 6, ASTM N330 was used as the carbonblack, and in Comparative Example 7, ASTM N339 was used as the carbonblack.

TABLE 1 Compounding Amount (parts by mass) Natural Rubber 100 CarbonBlack 50 Stearic Acid 3 Zinc Oxide 5 Cross-Linking Promoter NS*¹ 1Sulfur 1.5 Note *¹N-t-butyl-2-benzothiazolylsulfenamide

TABLE 2 Comp. Comp. Comp. Comp. Comp. Comp. Comp. Comp. Ex. 1 Ex. 2 Ex.3 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 8 Ex. 9 Ex. 10 Production Air kg/h1198 1195 1190 1201 1196 1194 1195 1192 1196 1194 1194 Introduction FlowPreheating ° C. 679 677 680 681 681 678 678 675 678 677 675 TemperatureFuel Introduction kg/h 57 57 55 57 56 55 56 55 56 56 55 Flow Raw OilIntroduction kg/h 298 302 325 294 302 307 355 304 285 304 297 FlowPreheating ° C. 198 196 189 200 197 191 185 197 204 195 198 TemperaturePotassium Content ppm 0 10 0 0 3 0 0 20 0 22 0 Cooling Water Flow L/h150 145 120 130 130 155 145 170 140 142 145

Measurement of CTAB Surface Area

The CTAB surface area was measured in compliance with the method in ISO6810.

Measurement of 24M4DBP Oil Absorption

The 24M4DBP oil absorption was measured in compliance with the method inISO 6894.

Calculation of N₂SA/IA

The nitrogen adsorption specific surface area (N₂SA) was measured with asingle-point method in compliance with ISO 4652-1, and the iodineabsorption number IA was measured in compliance with the method in ISO1304. The ratio thereof, N₂SA/IA, was then calculated.

Measurement of TINT (Tint Strength)

The TINT (tint strength) was measured in compliance with the method inISO 5435.

Manufacture and Assessment of Tires

Using the rubber compositions manufactured as above in the tire tread,11R22.5 truck tires were manufactured by vulcanization at 150° C. for 45minutes, and the abrasion resistance, rolling resistance, factoryworkability, and chipping resistance of the tires were assessed with thefollowing methods. Tables 3A to 3C list the results.

TABLE 3A Comp. Comp. Ex. 1 Ex. 2 Ex. 3 Ex. 1 Ex. 2 CTAB (m²/g) 100 91 72109 92 24M4DBP (cm³/100 g) 101 88 104 107 96 TINT (%) 117 119 102 114115 N₂SA/IA 0.94 0.93 0.93 0.93 0.98 TINT + 0.4 × 107 109 108 102 10724M4DBP − 0.5 × CTAB Abrasion Resistance 122 112 110 119 111 IndexRolling Resistance Index 104 102 96 108 103 Factory Workability 113 103101 119 109 Index (ML₁₊₄) Chipping Resistance 115 116 105 107 104 Index(Tensile Test of Elongation at Break)

TABLE 3B Comp. Comp. Comp. Comp. Comp. Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7CTAB (m²/g) 88 56 90 78 90 24M4DBP (cm³/100 g) 100 102 68 86 101 TINT(%) 108 91 121 100 111 N₂SA/IA 0.93 0.97 0.98 0.99 1.03 TINT + 0.4 × 104104 103 95 106 24M4DBP − 0.5 × CTAB Abrasion Resistance 111 78 88 100113 Index Rolling Resistance Index 104 89 103 100 104 FactoryWorkability 111 78 88 100 111 Index (ML₁₊₄) Chipping Resistance 107 88121 100 103 Index (Tensile Test of Elongation at Break)

TABLE 3C Comp. Comp. Comp. Ex. 8 Ex. 9 Ex. 10 CTAB (m²/g) 117 90 10224M4DBP (cm³/100 g) 102 66 115 TINT (%) 125 127 113 N₂SA/IA 0.93 0.940.93 TINT + 0.4 × 107 108 108 24M4DBP − 0.5 × CTAB Abrasion Resistance123 90 127 Index Rolling Resistance Index 116 104 106 FactoryWorkability 133 93 133 Index (ML₁₊₄) Chipping Resistance 116 127 104Index (Tensile Test of Elongation at Break)

Measurement of Abrasion Resistance Index

The above truck tires were mounted on a vehicle, and after running40,000 kilometers, the amount of reduction of the tire grooves wasmeasured and is listed as an index, with the inverse of the groovereduction amount of the tire according to Comparative Example 6 set to100. A larger index indicates better abrasion resistance.

Measurement of Rolling Resistance Index

The above truck tires were allowed to rotate freely on a drum, androlling resistance was measured and listed as an index, with the rollingresistance of the tire according to Comparative Example 6 set to 100. Asmaller index indicates smaller rolling resistance, which is better.

Measurement of Factory Workability Index (ML₁₊₄)

The Mooney viscosity (ML₁₊₄) of an unvulcanized rubber compositionsample was measured at 130° C. in compliance with JIS K6300 and listedas an index, with the value for Comparative Example 6 set to 100. Asmaller value is better.

Measurement of Chipping Resistance Index (Tensile Test of Elongation atBreak)

In compliance with JIS K6251-1993, a tensile test was conducted on avulcanized rubber composition sample (vulcanization time: 30 minutes at145° C.), and the elongation at break (Eb) was measured at 23° C. andlisted as an index, with the value for Comparative Example 6 set to 100.A larger value is better.

Tables 2A to 2C show that using a rubber composition including 20 partsby mass to 100 parts by mass of carbon black combined with 100 parts bymass of a rubber component, the carbon black having a CTAB surface areaof 60 m²/g to 105 m²/g, a 24M4DBP oil absorption of 70 cm³/100 g to 105cm³/100 g, a N₂SA/IA of 0.95 or less, and satisfying Expression (1),allows for the manufacture of a tire tread in which the abrasionresistance, rolling resistance, factory workability, and chippingresistance have been simultaneously improved.

REFERENCE SIGNS LIST

1: First region (combustion region)

2: Second region (tapered region)

3: Third region (reaction region)

4: Choke

5: Narrow cylindrical portion

6: Wide cylindrical portion

7: Raw material inlet

7-1 to 7-3: Raw material inlet

8: Reaction stopping fluid inlet

8-1 to 8-5: Reaction stopping fluid inlet

1. A rubber composition comprising 20 parts by mass to 100 parts by massof carbon black combined with 100 parts by mass of a rubber component,the carbon black having a CTAB surface area of 60 m²/g to 105 m²/g, a24M4DBP oil absorption of 70 cm³/100 g to 105 cm³/100 g, a N₂SA/IA of0.95 or less, and satisfying Expression (1).TINT (%)+0.4×24M4DBP oil absorption (cm³/100 g)−0.5×CTAB surface area(m²/g)>106   (1)
 2. The rubber composition according to claim 1, whereinthe carbon black has a CTAB surface area of 90 m²/g to 105 m²/g.
 3. Therubber composition according to claim 1, wherein the carbon black has a24M4DBP oil absorption of 85 cm³/100 g to 105 cm³/100 g.
 4. A tirecomprising a tire tread manufactured using the rubber compositionaccording to claim 1.